The present invention relates to a method and an apparatus for designing a printed wiring board, and more particularly to a method and an apparatus for designing a printed wiring board in which the optimum grade of the board can be selected.
There are several kinds of printed wiring boards, such as glass cloth epoxy boards and build-up boards, that are distinguished by board formation techniques. Further, among these several kinds of boards, there are several types, such as xe2x80x9c4S2Pxe2x80x9d (4 signal layers and two power layers), and xe2x80x9c6S2Pxe2x80x9d (6 signal layers and 2 power layers), etc. that are distinguished by design criteria (design rules). Depending on the kinds and types of the boards, design rules including conductor width, wiring spacing, spacing between lands and conductors, the configuration of a wiring layer, the size of via holes that establish connections between conductors in different wiring layers, land size, methods of forming lands and via holes, and wiring density may vary. The boards can be graded according to their corresponding wiring densities. A board having a high wiring density is defined as a high-grade board, whereas a board having a low wiring density is defined as a low-grade board. Therefore, a high-grade board has more signal lines per unit area than a low-grade board. A higher-grade board also has a higher degree of flexibility in wiring than a lower-grade board if both are equal in size and the number of wirings, so that wiring patterns can be more easily formed on the higher-grade board in a shorter design time. However, in order to narrow the wiring width and spacing, and to reduce the sizes of via holes and lands, a more precise production technique is required, typically resulting in a corresponding increase in costs to produce such boards.
A grade of a printed wiring board is selected from among several alternatives by a designer thereof based on his/her own experience. Such an empirical selection of the board may often lead to a selection of an unnecessarily higher-grade board or a lower-grade board whose grade is too low to form wiring patterns thereon. Selection of an unnecessarily higher-grade board leads to higher production costs. On the other hand, selection of an unnecessarily lower-grade board renders the formation of wiring patterns impossible, whereby the grade of the board has to be selected again to accommodate such wiring patterns.
An object of the present invention is to determine the ratio of a total length of wiring which can be formed on the board to a total length of wiring which must be formed on the board, and to select an optimum grade of the board based on this ratio. It is another object of this invention to provide an apparatus and method for making a printed wiring board having the selected wiring thereon.
An apparatus for designing a printed wiring board according to the present invention comprises structure for obtaining an actual board area, obtaining an area of the board on which wiring patterns cannot be formed (hereinafter referred to as xe2x80x9cunwirable areaxe2x80x9d) and for determining the ratio of a total length of wiring which can be formed on an area obtained by subtracting the unwirable area from the actual board area (hereinafter referred to as wirable area) to a total length of wiring necessary to establish a connection between components.
A method for designing a printed wiring board according to the present invention comprises the steps of obtaining an actual board area, obtaining an unwirable area of the board, and determining the ratio of a total length of wiring which can be formed on a wirable area obtained by subtracting the unwirable area from the actual board area to a total length of wiring necessary to establish a connection between components.